Method of cutting flexible couplings



y 8 1956 c. w. BELDEN ET AL 2,744,449

METHOD OF CUTTiNG FLEXIBLE COUPLINGS Original Filed Oct. 30, 1950 6 Sheets-Sheet 1 2 INVENTORS y 8, 1956 c. w. BELDEN ET AL 2,744,449

Original Fi l e d 0 c t 3 0 l 9 50 p A"? m y 8, 1956 c. w. BELDEN ET AL 2,744,449

METHOD OF CUTTING FLEXIBLE COUPLINGS Original Filed Oct. 30, 1950 6 Sheets-Sheet 5 May 8, 1956 c. w. BELDEN ET AL 2,744,449

METHOD OF CUTTING FLEXIBLE COUPLINGS Original Filed Oct. 30. 1950 6 Sheets-Sheet 4 t I C F27. Z2

y 1956 c. w. BELDEN ET AL METHOD OF CUTTING FLEXIBLE COUPLINGS Original Filed Oct. 30, 1950 6 Sheets-Sheet 5 BY C ar/ a ATTORNEY y 1956 c. w. BELDEN ET AL METHOD OF CUTTING FLEXIBLE COUPLINGS 6 Sheets-Sheet 6 Original Filed 001:. 30, 1950 thenatureofsspline connections. I

Axial. misalignment of the shafts to becoupled will be 2,744,449 METHOD OF CUTTING FLEXIBLE COUPLINGS .CharlesW; Belden'and Harley E. Northrop,

Westfield, N. Y. I Original applicatiomOctoberSll, 1950, Serial No. 192,954. .Doigided andthis application July 21, 1952,..Serial N0. 3 ,044

2 Claims. --(Cl.- 90-4) Thisinvention relates to couplings of the class for coupling together rotary shafts that are outof axial align- ,teeth on the ring'gear; and thepresent invention is an improved coupling of this type.

, Such couplings are usually referred to as geartype couplings; becausethe teeth on the said parts may be conveniently-formed'by, gear-tooth cutting machinery, and because the parts considered alone resemble toothed gears. Infact, however, the characteristic action of gears,

, that is,.a pitch circle of one rolling on a pitch circle of v the other, is entirely absent in thecoupling; all of the I teeth and toothlspaces of.the'saidlouter toothed part of the coupling being at,all times intermeshedv with all of the teeth and tooth spaces of the said two inner parts in present whenltheirnaxes are at. an angle to eachother;

' or when they are. parallel but offset laterally, one from the other; or, .whenithey. areratan angle and alsoolfset.

- When two shafts,.. in axial misalignment of either of saidtypes are coupled by such a coupling the medial plane of the inner ,gear. or. ge ars) is. at anangle to the medial plane of the outer gear, (as .will be shown hereinafter),

, that is, the inner gear is tipped angularly withinthe outer gear, and in the absence of special provisions the teeth of the inner gear will bind in the teeth of the outer gear.

This would present no difiicult problem if the angled shaft misalignment could be selected or predetermined and be always the same; because it could be solved simply by providing suflicient clearance between the teeth of the two meshed gears. But the coupling to be practicable and commercial must be adapted to couple shafts of different misalignment angles in different installations; and in fact the actual angle is almost always unknown. An angle of misalignment greater than 3 is visibly apparent, and can usually be partially corrected or reduced, so that in general a coupling will have sufficient range of adaptability if it can couple shafts at all angles from to 3.

In toothed gear practice generally, it is desirable to provide a small clearance between the meshed teeth; and such clearance is also desirable betweenthe teeth in a gear type coupling. The small amount of lost motion introduced by such clearance is harmless and negligible.

However, in a gear type coupling, if the teeth are given enough clearance to allow the inner gear to'be tipped enough, as aforesaid, to couple shafts at an angle of misalignment as great as 3 then, when used to couple shafts at a lesser angle of misalignment, with the inner gear I United States Patent if the special form of teeth permits the gear to tip as aforesaid and without back-lash lost motion or binding, for one degree of misalignment and tipping, it will either cause binding or introduce back-lash lostmotion at other degrees. So far as is now known, noform of tooth has heretofore been devised which will obviate 'thesedefects.

Perhaps the most completely-developed prior coupling of this type is one in which the inner gears are spherical gears, that is, haveteeth .cutwith respect to a spherical pitch surface, to allow-the inner gear to tip without binding; but as will appear hereinafter, a sphericalgear does not solve thewdouble .problem 'of no binding and no back-lash lost motion.

The. objects of "the, invention are:

To provide generally an improved coupling of the type referred to, bywhich shafts at any angle of misalignment from 0 to 3 or higher if wanted, can be coupled and driven without binding and without backlash lost motion in. the coupling.

To provide for a couplingof the type referred to, an improved shape of tooth at the aforesaid spline connection of the parts by which backlash lost motion or binding as referred to, may be,obviated. 1

Other objects will become apparent to those skilled in the art to which the invention; appertains.

The invention itself is setforthin. the appended claims.

Generally speaking, the preferred embodiment of the invention described herein is a coupling ofthetype referred to, and comprising an outer ringgear, with internal teeth parallel to its; -axis;..and. an inner gear the teeth of which on the opposite sides of a medial plane of the gear, converge rectilinearly toward points .on the gear axis, that is, lie on opposite cone surfaces whose bases are in the medial plane and whoseapexes. arein the-gear axis.

.The teeth. of .the inner @gear are preferablyvcut from a blank bya gear cutting hob, .with generating relative motion of the hob and blank, which makes the faces of the .teethgenerally of involute..form, although the involute .,shape of;the faces is.incidental and not essential.

The teeth, being generated teeth, may beconsidered as having a chosen pressure anglepredetermined orselected by the hob and thegenerating motion etc, as in the case of ordinary gears as such.

The angular displacement of the shafts to be coupled which maybe encountered in practice may'also be chosen.

The pitch' diameter. of: the gearmay also be chosen, as represented by a circle .on the teeth at their middle between root and tip.

Given the maximum angle of misalignment and the pressure angle and the pitch diameter; the cone angle and other factors may be determined from a formula to be described by which a coupling can be made that will have 1110 back-lash lost motion or binding ,at all shaft misalignment angles from the zero to the chosen angle.

As will be referred to a maximum shaft misalignment angle of 3 will sufficefor most installations, but as will be found, misalignment angles -up-to or even greater than 6 are possible with the invention without back-lash lost motion or binding.

The invention is fully disclosed-in-the following de- 3 scription taken in connection with the accompanying drawing, in which:

Fig. 1 is a longitudinal sectional view of a coupling embodying the invention in one form, and showing two shafts coupled together without misalignment for simplification:

Fig. 2 is an end elevational view of the coupling of Fig. 1;

Fig. 3 is a fragmentaryview similar to a part of Fig. 1 illustrating parts as they appear when one of the shafts is at an angle of misalignment with respect to the other;

Fig. 4 is a diagrammatic view illustrating methods of cutting teeth on an inner gear element of Figs. 1 to 3;

Fig. 5 is a fragmentary view to enlarged scale of an upper part of Fig. 1 illustrating meshed teeth on an outer and an inner gear gear element of Fig. 1;

Fig. 6 is a view illustrating the teeth of Fig. 5 as viewed from above;

Fig. 7 is a view illustrating the teeth of Fig. 5 as viewed from the end;

Fig. 8 is a cross sectional view of the teeth of Fig. 5 taken from the plane 8-8 of Fig. 5;

Fig. 9 is a cross sectional view from the plane 9-9 of Fig. 1;

Figs. 10 and 11 are views similar to Figs. 8 and 5, but

illustrating meshed teeth of the inner and outer gears when the inner gear is tipped with respect to the outer gear;

Fig. 12 is a view similar to Fig. 1 illustrating another embodiment of the invention;

Figs. 13, 14, and 16 are views illustrating the form of Fig. 1 diagrammatically and showing the positions taken up by parts thereof under difierent conditions of shaft misalignment;

Fig. 17 is a diagrammatic view illustrating another form of embodiment of the invention;

Figs. 18 to 23 are a group of views in general similar to the group of views Figs. 5, 6, 8, and 10, illustrating teeth of the prior art;

Fig. 24 is a view similar to Fig. 4 illustrating a modification.

Referring to Fig. 1, there is shown at 1 and 2, two shafts coupled together by the flexible coupling embodying the invention. For simplification, the shafts are shown with their axes 3-4 in alignment. A coupling hub member 5 is mounted on the end of the shaft 1 by a key 6 and set screw 7. A hub member 8 is mounted on the shaft 2 by a key 9 and set screw 10, the two hub members being preferably alike and mounted reversely on the shafts.

On the hub member 5 is an annular rib or disc like peripheral portion 11 on which are gear teeth 12 to be described, the rib and teeth constituting what may be referred to as an inner gear 13. The hub member 8 has a like rib 14 and teeth 15 constituting an inner gear 16.

Surrounding the inner gears 13 and 16 is a tubular sleeve 17 on the inner wall of which are formed at one end portion elongated teeth 18 meshed with the inner gear teeth 12 and at the other end portion, elongated teeth 19 meshed with the inner gear teeth 15; and the sleeve 17 and its teeth 18 and 19 may be referred to as an outer gear 20.

The teeth 12-15 of the inner gears 13 and 16 fit the tooth spaces of the outer gear 20 in such manner that the outer gear is supported thereon, see Fig. 9.

At the opposite ends of the hubs 5 and 8 they have cylindrical surfaces 21 and 22. Surrounding these surfaces but spaced radially therefrom as at 23-24 are annular end plates 25 and 26 mounted on the ends of the sleeve 17 by screws 27-27.

The teeth 18-19 of the outer gear 20 terminate short of the ends of the sleeve 17 leaving annular grooves 28-29 between the plates 25-26 and the teeth 18-19.

Annular seals 30-31 of rubber preferably of a kind resistant .to chemical action of oil, for example Neo- 4 prene," are provided between the said cylindrical surfaces 21-22 of the hubs and the sleeve 17. They comprise outer annular beads 32-33 bottoming in the said grooves 23-29, and clamped between the rings 25-26 and the ends of the teeth 18-19 and thereby effecting seal with the sleeve 17.

The seals have annular flexible skirts 34-35 inclined inwardly radially and inwardly axially, terminating in annular beads 36-37 encircling the hub surfaces 21-22. Coiled springs 38-39 of the annular garter spring type encircle the beads 36-37 and constrictingly hold them upon the surfaces 21-22 to efiect seal thereat.

A sealed chamber 40 is thus provided in which a quantity of lubricating oil is entrapped and sealed and thrown outwardly into an annular body of oil on the inner side of the sleeve 17 by rotation of the parts in use, flooding and lubricating the meshed teeth.

The flexibility of the seal skirts 34-35 permits angular misalignment of the shafts 1-2 and tipping of the hubs 5-8 (to be referred to) while maintaining the seal.

The axially inner ends of the seal beads 36-37 are spaced from the ribs 11-14 being opposite annular pockets 43-44 in the ribs, allowing freedom of the outer gear 20 to float and shift axially relative to the inner gears 13-16 without contacting the beads 36-37 and the extent of the shifting is limited or stopped in either direction by abutting contact of the teeth 12 and 15 with the outer beads 32-33.

Oil may be introduced into the chamber 40 after assembly of the coupling with the shafts, through a screw plug 45 in the wall of the sleeve 17.

In operation, the shaft 1 when rotating drives the inner gear 13; its teeth 12 meshed with the teeth 18 of the outer gear 20 drive the latter; the teeth 19 of the outer gear meshed with the teeth 15 of the inner gear 16 drive the latter; the inner gear 16 drives the shaft 2. The parts are shown in Fig. l with the shafts 1 and 2 in axial alignment.

In Fig. 3, the shaft 1 is shown with its axis 3 at an angle of misalignment, a, with respect to the axis of the shaft 2 (not shown) and the inner gear 13 is shown at the corresponding tipped angle with respect to the outer gear 20 as the parts would be in practice in an illustrative case; and the following description explains the coupled drive and its property of driving without back lash lost motion at all such angles of misalignment.

The teeth on the inner gears, for example the teeth 12 on the inner gear 13 are cut from a solid blank as illustrated diagrammatically in Fig. 4.

A disc like circular blank 46 has its peripheral portion bevelled in opposite directions from its medial plane 47, as at 48-49, so that the surfaces 48-49 lie on opposite cones 50-51, having the medial plane 47 as their common base, and having their apices 52-53 in the axis of the blank.

The angle 12, between the side of the cone and the axis 54 will hereinafter be referred to as the cone angle. A helical hob 55 is rotated and fed parallel to the side of the cone 50 along the line 56 cutting the blank from the right face as viewed in Fig. 4 to the medial plane of the blank, and then a hob 55A is fed parallel to the side of the cone 51 along the line 57 cutting the blank from the left face to the medial plane 47. Alterna tive methods will be referred to later.

The blank is concurrently rotated on its axis 54 at a suitable speed for the hob so that the hob cuts generated teeth with involute faces, in the same manner as ordinary involute gear teeth are cut and generated on gears that are to be used as gears.

The teeth thus made will have the form shown in Figs. 5 to 8, where one of them 12 is shown to enlarged scale meshed with a tooth space 58 of the outer gear teeth 18.

The involute faces of the teeth 12 indicated at 59, Fig. 7, will taper from the root toward the tip and may Jae consideredas,havingapressure angle, as ifthey iwere to be used as ordinary rolling gear teeth, the-pressure angle having been preselectedbyihe shape or angle of the helical hob teeth.

In Figs. 5 to 8, the tooth 12 f the inner gear 13 is shown. in the condition of the parts of Fig. 1 without misalignment angle, and therefore "with-"the gear not tipped as referred to, and, as seen, the tooth face (toward-"the observer in'Fig 5) is in two halves 60-61 meeting 'ina dihedral edge or corner "62 atthe medial plane; and the opposite face (Fig. 6) likewise has two halves 63-64 meeting in a dihedral edge 65. As viewed in'Fig. 5, all parts of -the-tooth slope rectilinearly from themedial plane toward the opposite ends of the tooth, at the cone angle b.

The teeth' l8 of the outer gear'20'are cut by the usual internalgear cutting method and parallel to the axis, at a pressure angle such that the teeth 12 of the thickest -pa1t=of the inner gear teeth at the dihedral angle edge '62'65 conformto and substantially fit-the tooth spaces -58-of-the outer'gear teeth asshown in Fig. 9.

'The'faces of the tooth inthe direction parallel to the gear axis and parallel to theteeth spaces 58 of=the outer gear, are rectilinear as shown in Fig. 8 for the section'plane =8-8 of Fig. 5;* and this illustrates'one of the most important features of the invention to be :more fully described;- but here it ispointed out that as "illustrated in" Fig. 8, even -if*the.tooth"12'fits the tooth space 58-so intimately thatthe points 66-67 on the 'said dihedral' c0rners 62-'65 of the toothare in actual contact with the tooth'faces -68--69z of theteeth-18, then 'because-of-thecone angle at which the teeth are formed,

the faces61-to 64 of the-teeth 12 all incline away from the sides 6869 of the tooth faces '-ofthe-outer gear in rectilinear directions, at both sides of the dihedrah edge- -points-66-'67.

"Referring nowtoFig.'"9, in which the inner gear 13 is shown as -in 'Fig. l, withoutbeingtippedclue to shaft 1 misalignment, and with itsteethIZ meshed in the tooth spaces' -58 'betweenthe teeth'18 of-the outer -gear'20 1 iti-is :convenient to designate-the -top,-bottorn, and sides of-the-inner gear, asVieWed, -by-the characters'A, B, C, and: D.

' "=In :thisnn-tipped position- -of the inner gear 13, the

7 teeth- 12: atall zfourpositions'A to'D, willbeinthe relation to the outer gear teeth spaces, as illustrated in t Figs.-"i5=.-tog 8: "Theteeth '12- can be made, as will be ...understood,i-by setting -the hob '-55, Fi'g. 4, at a suitable .cutting depth,-.so-that in FigssS. to 8; the dihedral edges -;62.:an'd-65 of theinner gear 13 :willbe in actual contact -.withthe sides .68 and 69 r ofthe teeth 18 of the outer .iigear, that is, without: anyclearance -therebetween. All of the teeth 12 of the-inner -geanwillmeshwith and i engageand-idrive. the teethdfiof the outer gear.

tWhenwthe shafts .areat amisalignment angle a, as re- .=f'erredn-to,=.the inner1gear 13.is tipped-within'the outer mgear 20.;as in'Fig. 3. i In'Fig'. 9,the topA isthennearer ;to ;the observer, thebottomiB farther away from the .'.observer; and'thepartsIC. and D-are rocked on a horizontal .axis..67, rocking or: twisting the inner teeth 12,1

; ontthatuaxis.

tIr1\Eig::3,::this rockedortwisted positionof the tooth 12 at the position C shown in dotted lines and'as seen it: liesadiagonally in the. tooth space58: of the I outer gear 720; and itlJlS twisted-positionis also shown more clearly,

6 :p ivotingaround thepoint. 66,. and-movingeina circular arc, and as introducing. aslight amount of .clearanceat the point 67.

The maximum anglethroughwhich the tooth: 12 can twist in this manner canbe made to be at least as great as the maximum angle ofshaft-misalignment to be encountered, and causing the twist, by providing a suitable cone angle as willbe explained.

In Fig. 10, the tooth. 12 isvshown as twisted through the aforesaid angle a.

The foregoing total possible tipping of thegear 13 and twisting of tooth 12 at positions ,0, andD, assumes that the gear 13 is free to tip without binding at any point.

This will be true for the teeth v12 at positions A and B, Fig. 9 because their arcuate movement around the axis 67 upon tipping of the gear on the axis will be generally parallel to the tooth spaces 58 of theouter gear in which they are meshed, and they will take up positions such as shown in Fig. 11 for the position A.

This arcuate movement will have a component toward the axis 67 and the dihedral edges of the tooth will be withdrawn slightly, radially, outof the tooth spaces 58 and not be in actual contact at said positions A and B. 1

At positions in Fig.9 between positions A and D (and similarly between positions D B and BC and C-A) tipping of the inner gear and rocking its teeth around the axis 67 gives the teeth, a componet of movement toward the observer in Fig. 9 and. a component vertically downward as viewed in Fig. 9 which later tends to make the teeth 12 engage and bind on the outer gear teeth 18 andlimit the said tipping angle (assuming that the inner and outer gear teeth' were in actual contact at the di-' hedral edges 62 and'65 in the nontipped position).

It can be demonstrated by trigonometry that the point between positions A'and D for example, at which this binding tendency is greatest depends upon the pressure angle chosen for the teeth, beingvnearer to the position D for larger pressure angles and farther away from D for smaller. pressure angles, approaching a position midway between A and D for zero pressure angle.

The teeth 12.will therefore be cut to provide relief to prevent this binding, to permit tipping of the inner gear through the maximum angle as aforesaid, and this is done by simply setting the hob to cut deeper.

A very slight amount of such relief cutting is needed 'for this purpose, less being required for teeth of large pressure angle than for teeth of small pressure angle.

After such relief cutting is provided, the teeth 12.will be at actual contact with the teeth 18 insaid intermediate positions when. the gear is fully tipped; but the teeth 12 will be thinner at the dihedral corners 62-65 in the medial; plane, and this tends to introduce clearance thereat. When the inner gear therefore is in the nontipped condition, this clearance will appear at points 6667, Fig. 8,--and at all of the teeth around the gear; and when thegear isin the fully tipped condition, clearance will appear at thepoints 66-67, Fig. 10.

But this clearanceis still in all cases negligibly small, being less in fact than would be. occupied by a lubricating oil film, as will be shown,and will introduce no back-lash lost motion.

Since it is contemplated that the .teeth are to be lubricated by oil, and since if the teeth were cut as above described, the clearance at all teeth and in all positions is less than the thickness of an oil filin, the hob must now be set to cut still deeper to provide clearance and enough for oil films to form and be maintained on the teeth.

In the foregoing for description purposes, and as stated, the teeth 12 on the inner gear 13 were considered as they would be if out so as to be in actual contact all around the. gear at; the. dihedral edges 62-65 (Figs. 5 to 8) in the intermediate positions (between A and D etc); and then further out to provide oil film clearance. In practice, of course, all of this cutting would be done at one operation with a single depth setting of the hob.

When the inner gear is tipped through the maximum angle, corresponding to the maximum shaft misalignment angle, that may be encountered, the gears drive at the teeth that are in said intermediate positions, between A and C etc., because the clearance is then the least at those positions.

For smaller and smaller angles of misalignment and less and less tipping of the inner gear, the position around the gear at which driving occurs spreads over more and more teeth both clockwise and counterclockwise from said position, taking in more and more teeth until at Zero tipping angle, it extends all the way around the gear and driving occurs on all of the teeth and the clearance is then at the maximum.

Just how little the aforesaid clearance is, including that necessary to prevent binding at the said intermediate positions plus enough to provide room for oil, can be ascertained from the following deductions: which also provide data for making a coupling free from back-lash lost motion or binding as contemplated by the invention.

To design and make a coupling embodying the invention and having the above described advantages, certain assumptions will be made as follows.

Assume that the maximum shaft misalignment angle to be encountered will be 3.

The maximum tipping angle of the inner gear and the maximum twist angle of the inner gear tooth as in Fig. 10 will then be 3.

The tendency to bind at the four intermediate positions between A and D (D and B etc.) and for which relief is provided, will be greater for small pressure angles of the inner gear teeth than for large, and, corresponding to spur gear tooth practice the pressure angle may be in the range from 14 to and will be assumed here to be 25 The said tendency to bind will also be greater for large inner gear diameters than for small diameters and a gear of 4 diameter will be assumed, the diameter being taken at a point on the gear teeth corresponding to the pitch diameter of ordinary spur gear teeth and at, say, the middle of the teeth radially considered.

Let G equal the intermediate point for example the point between A and D, Fig. 9, at which maximum interference and binding tends to occur, when the gear tips the maximum due to-misalignment angle, G being measured in degrees from the position A.

Let H equal the maximum shaft misalignment angle to be encountered; and it therefore also represents the maximum angle of twist of the gear tooth as in Fig. 10.

Let I equal the pressure angle of the inner gear teeth.

Let X equal the amount of metal in inches that must be removed from the side of the tooth to prevent binding at the point G at maximum tipping of the gear.

Let PD equal the pitch diameter of the gear.

Let Y be a constant equal to the cotangent of the pressure angle and having values as follows:

Let F equal the cone angle at which the teeth are to be out.

From the foregoing the following can be shown,

G equals Fequals H Y Solving for G, F, and X in the assumed case of pressure angle I equals 25; Y equals 2.14; H equals 3; and PD equals 4":

G equals 57.5

F equals 6.42

X equals .0017" The clearance will be maximum at .0017" in the nontipped position of the inner gear at 0 misalignment; and the clearance will be zero at the 57.5 position G between A and D for maximum misalignment of 3, and hence at this point enough clearance must be added to contain oil film for lubrication, say .002". This added oil film clearance will also appear as added to the clearance of .0017" for no-angle of misalignment conditions; making the maximum clearance at any condition .0037.

This small clearance, filled as it is with lubricant oil is too small to cause any back lash even at the maximum clearance condition of no misalignment angle, and is of course, as shown, even less at all misalignment angles, down to .002 at maximum misalignment angle. It is to be noted that in ordinary spur gear practice a clearance between teeth of .004 or even greater is provided, and will contain lubricant, and introduce no objectionable back-lash; and therefore of course the clearance of .0037 will introduce no objectionable back-lash in the present invention.

As stated hereinbefore perhaps the most fully developed coupling of this general class proposed heretofore is one in which an inner gear has teeth cut like the teeth of a spherical spur gear; and the improvement of the instant invention over such prior couplings will here be explained in connection with Figs. 19, 18, 20 and 21, which in the order named, correspond respectively to Figs. 5, 6, 8 and 10 above discussed.

In cutting teeth 70 on the spherical gear 71, the hob travels on a circle (instead of along two rectilinear lines at an angle, such as lines 56-57, Fig. 4). The faces of the tooth 70 will therefore be convexly curved as at 72- 73 in Figs. 18 and 20. If the teeth 70 are cut of such thickness, that when the inner gear is in the aforesaid nontipped position, Fig. 19, and the tooth 70 in the tooth space 76 of the outer gear is without twist, and so that there will be little or no clearance, the tooth 70 will be substantially in contact with the outer gear tooth faces at points 77--78, Fig. 20, which corresponds to points 66-77 of Fig. 8.

In the present invention when the inner gear became tipped and the tooth twisted in position as described, the conditions at the inner gear tooth changed from Fig. 8 to Fig. 10. With the spherical gear tooth, that would correspond to goin g from Fig. 20 to Fig. 21. But as will be seen in Fig. 21, this would be impossible because of the convexity of the tooth faces 72--73.

Assuming that the tooth face 72. remains in contact with the outer gear tooth face 74, the tooth in effect rocks on that face 74 and the point of contact 77, Fig. 20, shifts to 77A in Fig. 21, and the outer face 73 of the tooth would have to overlap into the metal behind the tooth face, 75 as indicated by the dotted line 79, and this is impossible.

Thus, if the tooth 70 fits the tooth space 76 without clearance before gear tipping, the inner gear cannot tip at all to allow for shaft misalignment as explained hereinbefore.

In order to allow it to tip, and to allow the tooth to twist, the tooth 70 must be cut thinner, for example as in Fig. 22, where as shown it will all be within the tooth space 76.

Now even if the tooth is cut as thick as possible so as to be in actual contact at points 77A and 78A as in Fig. 22, to eliminate back-lash lost motion at maximum shaft misalignment and maximum gear tip and tooth twist, then for smaller angles of shaft misalignment and little tooth twist as in Fig. 23, the thinness of the tooth 70 introtillltjifs a large clearance as at 80 with attendant back- Thus with the spherical inner gear, the coupling can only be designed for a very limited range of lshafttangleadisplacement without back-lash lost motion.

{The coupling of Fig. 1 is what maybe called a double form, the outer gear element or sleeve 17 beingsupported by'and floating on the meshed engagement of two sets of 5 teeth 18 and 19 with the teeth 12 and 15 of two inner gear elements 13 and 16 one on each of'the shafts land 2 to be coupled.

'In Fig. 13, this coupling is shown diagrammatically when-the two shafts 1 and 2 are substantially in axial 10 In Fig. 14, one shaft 2, is at an angle to the other shaft '1, and displacedlaterally with respect to it, so that all of the tipping angle is at the gear 13; and this case illustrates the importance of having no back-lash lost motion 20 in the non-tipped condition of the inner gear 16, as well as in the tipped condition of the gear, 13. Fig. 16 illustrates the conditions when the two shafts,

1 and 2 are parallel but offset laterally, one from the other.

Both gears 13 and 16 are tipped with respect to the outer n gear 17.

In Fig. 12 is illustrated a coupling in what might be called a single form. An inner gear 13 having teeth 12 is mounted on a shaft 1 and sealed by a'seal 30, ta l-substan- A,

The outer I course, be understood that the hob 55 may be fed in either tially of the same construction as in Fig. 1. gear teeth 18 are here on a sleeve 81'having a flange 82 by which it is secured by screws 83 to a flange 84 on a hub 85 mounted on the other shaft, here 2A. An oil chamber 86 is provided within the sleeve 81 and supplied through a duct 87 closed by a plug 88.

The coupling of Fig. 12, as will be apparent, may be used with the shafts 1 and 2A in the cases illustrated in Figs. 13 and 14 for the shafts 1 and 2.

In Fig. 17, is shown diagrammatically an arrangement using the coupling of Fig. 12 as auniversal joint construction in the line of two shafts 89 and 90, ofiset lateral- .ly and at an angle to each other.

In Fig. 17, a coupling 91 is provided which may be like the coupling of Fig. 12, the outer gear teeth 18 being on a sleeve 81 connected to a hub 85 on the shaft 90; and having an inner gear 13 with teeth 12 meshed with'the teeth 18.

A similar or like coupling 92 is mounted on the shaft 89, identified by the same part numbers with the suffix A.

The two inner gears 13 and 13A are connected together by a shaft 93.

The couplings are lubricated as described for Fig. 12 and sealed by seals 30-30A which may be the same as hereinbefore described.

A universal joint of this construction has the advantage that lubricant is not thrown out of it by centrifugal force as in the case of many prior joints, but is maintained thereby in an annular ring at the engaged gear teeth submerging them at all times.

It is believed that it willbe apparent that the arrangement of Fig. 17 may be used with shafts that are parallel but offset from each other; or, at an angle to each other and not offset.

To simplify the description of the process of Fig. 4, the blank 46 was described as having its periphery pre-cut to the cone angle. 7 This is not an essential step of the process. It is preferable for the periphery to be cut at some angle or rounded at each side of the medial plane in order that the tip surfaces of the teeth 9495 (see Figs. 5 and the blank periphery had been cylindrical.

In the process of Fig. 4 as will now be apparent, the

:h'elicalihob SSILmay be movedto approach .the b1ank=46' .along the 111185156 while another hob -55A.-is,1. PProaehing -.the:blank alongthe line ,57 at'the same time but. at. a .diflierent point around the blank.

; Onthe hobr55fafter ,approachingthe blank andcutting ,along;the line 56 may be gchanged indirection and moved along theline, 57 continuing to cut andfinally leavethe blank.

. Itis believed that, from the foregoing, it will be clear that. a part of the inventionof primary importance resides in providing teeth on the inner gear of suchform that a tooth may fit in a tooth space of the outer gear with no .more clearancetherewith than is necessary foran oil film,

in ordinary gear practice, when the inner gear is not tipped, as when there is no shaft misalignment; and at the same time when the inner gear is tipped by ,shaft misalignment will allow the inner gear teeth to twist in .the outer-tooth spaces without binding. The preferred way to effect such form is to provide the tooth faces of the inner gearwith-dihedral corners as at 6265, Figs. 5 -t.o 11,1or at 62A'Fig. 24.

Such teeth-canbe mademost conveniently, and efliciently by generating them as involute teeth with a helical hob;;and-,;feeding; the hob so that the cut teeth conform generally to thesurfaces of two opposing cones whose common base is at-the medial plane of the gear and whose .a iq sare in-the axis of the gear and for that reason the describ edprocess and theresulting gear are preferred.

. 111;.any of the above mentioned methods of cutting the teeth, for example with reference to Fig. 4 it will, of

direction along the line 56, that is, either toward or from the medial plane of the blank, the choice being determined by factors of design of the machine driving and feeding the hob.

In Fig. 4, When considered as illustrating the movement of a hob along the rectilinear lines 56 and 57, these paths of movement meet at a point 106, at which the lines of movement intersect.

However, in some cases, having in mind the design of amac'hine to drive and directionally feed the hob, it may be found advantageous to go from the direction 56 to the direction 57 (or vice versa) with a curved movement. This is illustrated in Fig. 24. The path of movement 56 proceeds rectilinearly to a point 107 and continues into the path 57 at a point 108 and between the points 107 and 108 the path-is curved, preferably circular, as at 109.

When this process is used, the dihedral angle corner or edge (see Fig. 5) will not be a sharply defined edge, but will be a slightly rounded, dihedral corner or small area 62A departing from a sharp dihedral corner by a few ten thousandths of an inch; but for all practical pursary. limitation that the medial plane be exactly midway between the faces of the blank or exactly midway between the opposite ends of the teeth; nor that it be exactly at right angles to the axis of the blank considered as circular;

nor that the apex of the cone be exactly in the axis of the blank;,as it is believed will be understood.

While his preferred to cut the teeth on the inner gears by atooth generating helical hob as described, it is believed that it may be apparent that they may be cut with a circular disc-like toothed milling cutter having suitably formed teeth, and. fed across the blank along the coneangle lines 56 and 57 of Fig. 4, without concurrently rotating the blank, and that those skilled in the gear cutting I art will know how to do this without further illustration or description.

' In cutting the teeth on the inner gear as described for ,the preferred process, the lines of direction of the cutting,

-will be understood without further illustration or description.

In such case the teeth would still be properly described as conforming in general to the surfaces of cones, whose apices are at opposite sides of the blank.

This application is divisional from pending application Serial No. 192,954, filed October 30, 1950, for Flexible Couplings.

We claim:

1. In connection with a flexible coupling of the type comprising an outer toothed element having a number of radially inwardly projecting outer teeth in a circular series around an axis of rotation, and an inner toothed element having a like number of outwardly radially projecting inner teeth in a circular series around an axis of rotation; the teeth of the outer element being parallel to its axis; and the teeth of the inner element all meshed with the teeth of the outer element and formed so that the two elements thus meshed may rotate on their axes withwhich includes: mounting a helical hob for rotational movement and feed movement; mounting a blank, having a disc like peripheral portion, for rotational movement; rotating the hob and blank at tooth generating relative speed and feeding the hob across the peripheral portion of the blank in a rectilinear feed direction, to cause the hob to cut generated teeth in the peripheral portion of the blank at a known pressure angle; guiding the feed of the hob to cause its said rectilinear feed direction to be at an angle to the axis of the blank equal to the said maximum angle multiplied by the value of the cotangent of the known pressure angle.

2. The method described in claim 1 and in which the said angle between the feed direction and the axis is at one side of the blank and the hob is fed toward that side of the blank and part way through it, and the direction of feed is then shifted to feed the hob through the rest of the blank with the said angle between the feed direction and the axis at the other side of the blank.

References Cited inthe file of this patent UNITED STATES PATENTS 2,164,643 Drader July 4, 1939 2,315,068 Matthews Mar. 30, 1943 2,464,963 Bregi ct al Mar. 22, 1949 2,473,709 Hitchcock June 21, 1949 FOREIGN PATENTS 629,317 France July 25, 1927 

